The Formation of Halonitromethanes in Wastewater Treatment Plant Effluents

摘要

The objectives of this work were to investigate the formation of Halonitromethanes (HNMs) atrnwastewater treatment plant effluents under different disinfection conditions, to study the effect ofrnultraviolet light (UV) disinfection in wastewater treatment facilities on HNM formation potentials, and tornquantify the actual occurrence of HNMs at the effluents of selected wastewater treatment plants. Thernresults showed that among the five disinfection scenarios tested, HNM yields per DOC were in the orderrnof ozonation-chlorination > ozonation-chloramination > chlorination > chloramination > ozonation.rnPre-ozonation prior to chlorination and chloramination significantly increased HNM formation, whilernozonation alone did not produce any HNMs. Therefore, HNM formation is expected to be problematicrnmainly in treatment plants using ozonation followed by chlorination. The use of chloramines afterrnozonation significantly decreased HNM formation compared to using chlorine after ozonation.rnChloramination produced the least amount of HNMs of all the disinfection scenarios tested. Despite somernof its disadvantages (e.g. weak disinfectant, nitrification problems in distribution systems), it appears thatrnchloramination produces significantly lower amounts of HNMs as well as regulated trihalomethanes andrnhaloacetic acids than chlorination. The typical UV disinfection conditions in full-scale municipalrnwastewater treatment plants (WWTPs) using low pressure lamps did not change the HNM formationrnpotential (compared to the same water prior to UV disinfection) in wastewater effluents. Also, actualrnHNM concentrations at the effluents of full-scale WWTPs using chlorine disinfection were below 2 μg/L,rnwhile no HNM formation was observed at the effluents of WWTPs using UV disinfection. It appears thatrnat the typical disinfectant doses and detention times of wastewater disinfection processes, trace amountsrnof HNMs will form. However, WWTPs still release HNMs (and other DBP) precursors, as observed withrnthe formation potential tests, to downstream users.